Strut Braced Wings

[lucy_b14]

Hi

Does anyone know the main advantages and disadvantages of strut braced wings on fixed wing aircraft, and why they are not used for any large commercial planes these days (as far as i know!)?

Thank you

[FredGarvin]

I can't really think of any advantages to running struts. I guess if you used struts you could use less/inferior materials for wing spars. The struts will have disadvantages of increased drag, complexity of building and they tend to break. Drag and strength would be a huge issue for a commercial aircraft. Really, there is no need to use struts with modern materials and designs in place.

[russ_watters]

The benefit would be that you could make stronger wings with less materials - so they'd be lighter. But as Fred was saying, lift/drag ratio is a (or the) critical factor in airplane performance.

[02TT]

Early aircraft had strut wings because engineers believed that thin wings promoted lift. Due to the especially thin design of the wing their was not enough internal room for adequate bracing for a wing span wide enough to carry the load, so they made two shorter wing with external bracing. As technology developed engineers discovered a thicker wing actually was more efficient making lift. This discovery was before air transportation was reliable and safe enough to be viable.

[cjsudz]

Strut braced wings are a reasonably new idea 'in the transonic airline world, although the idea is not a new one in general aviation and they were intitially used by early aircraft designers around the Wright brother's time on thin wings before the realisation that thicker cambered airfoils generated more lift at subsonic speeds due to induced circulation characteristics as said by the previous chap.' They've mainly been researched by Virginia Tech University (USA). Google their technical papers.

Advantages
The savings can be unbelievable on modern config airliners. 20% direct operating costs, 20% reduced specific fuel burn etc etc all on simulated mission proposals for boeing aircraft flying standard medium haul routes with built in strut brace.

Disadvantages/problems
The strut can cause massive interferance drag if badly designed. There is a paper into the for a Boeing 737 flying at 0.85 mach where the guy came up with formulas to predict the drag based on the strut connection angle at the wing. He concluded a perpendicular connection was best.

The strut must also not just deal with tension when aircraft is in cruise, but also compression of wing when it is on ground fully fueled. Various designs have been proposed within strut structures to deal with this.

Why haven't most airline manufacturers not jumped at the opportunity to put them on aircraft I hear you ask? The answer is strut bracing is only good for high wing aircraft (as strut is in tension during cruise = better for structural stability). Not many airliners have high wing aircraft. Companies such as cessna have experimented with struts however and been rather sucessful.

ps if you find information about the 'folding joints' necessary for strut braces in compression situations (such as the -2g taxi bump requirement) could you let me know?.

[02TT]

I got my information from a episode of Wings on the History channel. I guess their historians and virtually unlimited resource of technical data and aeronautical engineering advisor's are wrong.

[meestanbuscan]

Strut braced wings maybe coming to a comercial airplane near you . . . well in 25 years.

"With its Development of Subsonic Ultra Green Aircraft Research Project, Boeing Phantom Works—along with Boeing Commercial Airplanes, . . . — will evaluate the performance of these concepts with regard to noise, emissions, take-off field length, fuel use and energy utilization. "

Boeing's strut braced wing commercial airplane (http://www.aeronautics.nasa.gov/nra_awardees_10_06_08_f.htm)

[meestanbuscan]

A look at the concepts Boeing submitted to NASA for tomorrow's airplanes

Strut Braced Wing concept(Subsonic Ultra-Green Aircraft Research (SUGAR)) and supersonic concept (http://pw-mct-epw-app3.nw.nos.boeing.com/Public/EOTNewsNow/Story.aspx?StoryID=2119)

http://pw-mct-epw-app3.nw.nos.boeing.com/public/EOTNewsNow/Images/2119G266.jpg